Richard Sterba

Role of Mahaim fibers in cardiac arrhythmias in man.

Twelve patients with evidence of Mahaim fibers are reported, six with nodoventricular (NV) fibers and six with fasciculoventricular (FV) fibers. All patients with NV fibers had left bundle branch block morphology, and a sustained reentrant tachycardia with this morphology was proved in each case. In three of the six, ventriculoatrial dissociation occurred during tachycardia. We postulate that the mechanism of this tachycardia is a macroreentry circuit using the NV fiber for the antegrade limb and the His-Purkinje system with a portion of the atrioventricular node for the retrograde limb. ECGs of patients with FV fibers were varied, suggesting a functional relation to the right or left side of the septum. No direct relationship of FV fibers to observed arrhythmias could be found.

Esophageal pacing: a diagnostic and therapeutic tool.

The purpose of this study was to develop guidelines for reproducible esophageal pacing of the atria and to determine the incidence of successful initiation and termination of tachycardia using this technique in patients with a history of spontaneous supraventricular tachycardia (SVT). Strength-duration curves were performed in 39 patients using a bipolar esophageal lead with a 2.9-cm interelectrode distance. Unlike strength-duration curves normally obtained -in cardiac tissue, which plateau at pulse durations more than 2.0 msec, the esophageal current threshold decreased progressively as pulse duration was increased to the limit of the stimulator (9.9 msec). At pulse durations of 8.0-9.9 msec, atrial capture was achieved in all patients. At progressively shorter pulse durations, capture was achieved in progressively fewer patients despite use of current up to 30 mA. Stable pacing was achieved in 26 of 39 patients with a pulse duration of 1.0 msec (mean threshold 21 mA), in 33 of 39 patients with a pulse duration of 2.0 msec (mean threshold 18 mA), and in 39 of 39 patients with a pulse duration of 9.9 msec (mean threshold 11 mA). The current requirements did not correlate with the amplitude of the unipolar or bipolar atrial electrogram recorded in the group as a whole, but the lowest thresholds in individual patients occurred at the site where the largest and most rapid atrial deflections were recorded. In 38 patients with documented SVT, overdrive pacing from the esophagus was performed at cycle lengths of 240-400 msec using a pulse duration of 7.0-9.9 msec. Reciprocating tachycardia was induced in 35 of 38 patients and was terminated by overdrive pacing in 33 of 38 patients. Atrial fibrillation was induced incidentally in four patients; sinus rhythm returned spontaneously. Other effects included ventricular pacing in two, unmasking of latent preexcitation in three, induction of ventricular tachycardia by atrial pacing in two patients with a history of ventricular tachycardia, and phrenic pacing in one. We conclude that atrial pacing can be achieved from the esophagus with minimal discomfort in the majority of patients; that lower pacing thresholds can be obtained with the use of wide pulse durations (7.0-9.9 msec) and a bipolar electrode with wide interelectrode distance (2.9 cm); that rapid atrial pacing from the esophagus can be used to induce and terminate SVT for diagnostic or therapeutic purposes; and that esophageal pacing provides a convenient way to assess repeatedly the efficacy of long-term drug therapy and to screen patients for preexcitation syndromes.

The electrophysiologic basis and management of symptomatic recurrent tachycardia in patients with ebstein's anomaly of the tricuspid valve

Twenty-two patients with Ebsteins anomaly were evaluated because of recurrent tachycardia. A total of 30 accessory pathways were present in 21 of the 22 patients. Twenty-six accessory pathways were of the atrioventricular (A-V) type while four were Mahaim fibers. Multiple accessory pathways were present in eight patients. Twenty-five of the 26 accessory A-V pathways were right-sided, either in the posterior septum (12 pathways) or the posterolateral free wall (13 pathways); one patient with corrected transposition of the great arteries had a left-sided accessory A-V pathway in a lateral free wall location. Patients with accessory A-V pathways had a long minimal ventriculoatrial (V-A) conduction time during reciprocating tachycardia (192 +/- 47 ms) and usually showed a persistent complete or incomplete right bundle branch block morphology. At surgery, preexcitation was invariably localized to the atrialized ventricle. The long V-A conduction time during reciprocating tachycardia appeared to consist of late activation of the local ventricle in the region of the accessory pathway with a further delay occurring before excitation of adjacent atrium presumably due to conduction over the accessory pathway. Accessory A-V pathways were successfully sectioned with no deaths in 13 of 15 patients. On the basis of these data, certain electrocardiographic findings encountered in the study of patients with recurrent tachycardia should point to the possibility of associated Ebsteins anomaly: morphology of the surface electrocardiogram suggesting preexcitation of the right posterior septum or right posterolateral free wall as well as the combination during reciprocating tachycardia of a long V-A interval and right bundle branch block.

Mechanisms of regular, wide QRS tachycardia in infants and children☆

A regular wide QRS tachycardia was electrocardiographically documented in 32 patients aged 1 month to 18 years. The mechanisms of the tachycardia were evaluated using standard multicatheter electrophysiologic techniques. These mechanisms included (1) orthodromic reciprocating tachycardia with bundle branch aberration (seven patients), (2) antidromic reciprocating tachycardia using single (three patients), or multiple (three patients) atrioventricular connections (Kent bundles), (3) atrial flutter with ventricular preexcitation over accessory connections (eight patients), (4) reciprocating tachycardia using a nodoventricular connection (Mahaim fiber) (five patients), and (5) ventricular tachycardia (six patients). Regular side QRS tachycardias are not rare in pediatric patients. Their mechanisms can be quite complex, and electrocardiographic analysis with respect to QRS configuration, heart rate, or the presence or absence of ventriculoatrial dissociation is not sufficient for diagnostic purposes. Our results show that considerable understanding of the mechanism of regular, wide QRS tachycardias can be obtained by multicatheter electrophysiologic study. Understanding the mechanism is essential in order to make rational use of available therapeutic options.

Atrial pacing from the esophagus in the diagnosis and management of tachycardia and palpitations

Recent reports have emphasized the usefulness of programmed electrical stimulation of the heart for predicting the effectiveness of pharmacologic therapy of recurrent tachycardias and for determining the basis of recurrent palpitations. We used programmed electrical stimulation of the atrium from the esophagus to study 12 children (ages 1 to 13 years) with either electrocardiographically documented tachycardia (seven patients) or recurrent palpitations (five patients). Atrial stimulation from the esophagus initiated and terminated tachycardia in all seven patients who had a previously documented tachycardia. In five of these patients tachycardia could not be initiated after therapy with quinidine sulfate, and no recurrences have been noted in 12 to 18 months of follow-up. In two patients tachycardia could be reinitiated despite therapeutic quinidine levels, and tachycardia has recurred despite quinidine therapy. Atrial stimulation from the esophagus initiated tachycardia in four of five patients with a history of palpitations. Electrocardiographic documentation of tachycardia was beneficial, because it provided a basis for determining whether therapy for tachycardia was indicated, and in some instances provided an opportunity for patient education to permit-self termination without medication.

The Induction of Atrial Flutter and Fibrillation and the Termination of Atrial Flutter by Esophageal Pacing

In patients with Wolff‐Parkinson‐White syndrome (WPW), it is important to assess the ventricular response during atrial flutter or fibrillation since conduction across the accessory pathway during these atrial rhythms may cause hemodynamic impairment or life‐threatening ventricular arrhythmias. We have recently reported the effective use of an esophageal electrode in pacing the atrium. In this study we praspectively assessed the ability to induce atrial flutter and fibrillation by esophageal pacing in 23 patients with WPW or other electrophysiological abnormalities. An esophageal bipolar electrode with 29 mm interelectrode distance was positioned in the esophagus to record the most rapid and largest esophageal electrogram (mean distance of 36.6 ± 2.9 cm (SD) from the nares). Pacing was performed at cycle lengths of 40–340 ms (mean 166 ± 72), pulse durations of 7.0–9.9 ms, and currents of 10–25 mA. Atrial flutter alone was induced in 6 patients, fibrillation alone in 11 patients, and both arrhythmias in 5 patients, In one patient neither flutter nor fibrillation was induced by esophugeal pacing, and fibrillation was induced only with difficulty using intracavitary pacing. Of the 11 patients with flutter, the arrhythmia was terminated in 8 by esophageal pacing at cycle lengths of 160–220 ms fmean 176 ± 18 ms). All patients tolerated the procedure well with only mild to moderate discomfort. Therefore, esophageal pacing appears to offer an effective, well tolerated method of initiating atrial fibrillation and flutter and terminating atrial flutter and offers a potentially useful noninvasive method of following patients serially.

The force-interval relationship of the left ventricle.

The force-interval relationship the dependence of cardiac contractility on the rate and pattern of stimulation has been shown to be independent of preload, but sensitive to the inotropic and disease state of the heart. The force-interval relationship was evaluated for the left ventricles of 42 patients, ages 1.5- 20 years, during cardiac catheterization using a micromanometer pressure transducer-tipped catheter and an atrial pacing electrode catheter. The left ventricular (LV) minor axis was monitored echocardiographically, and the end-diastolic dimension (EDD) and posterior wall thickness (PW) were measured. Hearts were paced at a variety of basic cycle intervals, to (1/heart rate), and two test stimuli were introduced at various times during a pause in the regular stimulation (test intervals t, and t2 were measured relative to the last regular systole before the pause). For t, < to and t2 2 tl + to Pma of the second test systole was greater than Pma for the last regular systole before the pause (equivalent to postextrasystolic potentiation). The ratio of these values of Pmax (test to regular) for systoles with equal LVEDDs, the force-interval ratio, was used to characterize the relationship. Patients were divided into three groups: group 1 (n = 17) patients had normal LVEDD, LVPW and pressure indices. Group 2 (n = 17) patients had increased LVEDD or LVPW but normal pressure indices. Group 3 (n = 4) patients had increased LVEDD and depressed pressure indices. The force-interval relationship was similar for groups I and 2: Pmax increased monotonically with t, or t2. However, the force-interval ratio was larger for group 2. The relationship for group 3 was different. Pmaz was a biphasic function of the test interval, increasing for small values of t, or t2 and decreasing for larger values of t,. The force-interval ratio was smaller than or equal to unity for short values of t,. This postextrasystolic depression was never found in groups I or 2.

Catecholamine induced double tachycardia: case report in a child.

A six‐year‐old girl with syncope in association with atrial flutter‐fibrillation and ventricular tachycardia produced by exercise or emotion is presented. The tachycardias could be reproduced by low‐dose isoprolerenol infusion and were blocked by high dose propranolol therapy. Catecholamine‐induced tachyarrhythmias should be suspected in children with unexplained syncope in association with exercise or emotion.

Corrected transposition with severe intracardiac deformities with Wolff-Parkinson-White syndrome in a child. Electrophysiologic investigation and surgical correction.

This is a report of a 10-year-old child who underwent surgery for complex congenital heart disease consisting of corrected transposition of the great vessels, ventricular septal defect, patent ductus arterisus, severe left-sided atrioventricular (AV) valve insuffieicney (Ebsteins deformity) and Wolff-Parkinson-White syndrome. The site of his accessory AV connection was localized preoperatively at a left anterolateral site by isopotential body surface maps and by intracardiac electrophysiologic studies. He successfully underwent surgery for closure of the ventricular septal defect, ligation of the patent ductus arteriosus, replacement of the left-sided AV valve, and interruption of the accessory AV pathway. Unavoidable complete AV block acquired at surgery required subsequent permanent pacemaker therapy.

Heart block in children - Evaluation of subsidiary ventricular pacemaker recovery times and ECG tape recordings

SummaryTo evaluate subsidiary ventricular pacemaker function in 20 children with congenital or surgically induced complete heart block, we measured recovery times following overdrive ventricular pacing. Long-term ECG tape recordings were performed in eight of these children. Ages ranged fom 1 month to 17 years. The resting R-R intervals ranged from 595 to 1,740 msec. The ventricles were paced at various cycle lengths of 400 to 1,000 msec with either transvenous electrode catheters or surgically implanted epicardial electrodes. His bundle recordings showed that the site of block did not allow separation of patients with symptoms from those without symptoms. Prolonged recovery times were present in patients with block above the His bundle recording site who had symptoms of syncope or dizziness, as well as in patients who had a wide QRS. However, some asymptomatic patients with heart block above the His bundle recording site also had long recovery times. None of the asymptomatic patients who had ECG tape recordings had paroxysmal tachycardia in more than 300 hours of recordings. However, one symptomatic patient with congenital heart block and a prolonged recovery time had brief episodes of paroxysmal ventricular tachycardia that produced no symptoms at the time of recording. The results suggest that the coexistence of prolonged recovery times and paroxysmal tachycardia may be predisposing factors to the development of symptoms in patients with complete heart block. We believe that further electrophysiologic investigation of this possibility is warranted in patients with heart block.